In the manufacture of semiconductor devices and other products, ion implantation is used to dope semiconductor wafers, display panels, and other workpieces with impurities that create certain electronic properties for electronic components. Ion implanters or ion implantation systems treat a workpiece with an ion beam to produce n or p-type doped regions, or to modify the strain in certain regions, or to form passivation layers in the workpiece. When used for doping semiconductors, the ion implantation system injects a selected ion species to produce the desired extrinsic material, wherein implanting ions generated from source materials such as antimony, arsenic, or phosphorus results in n-type extrinsic portions in a semiconductor wafer, and implanting ions generated from source materials such as boron, gallium, or indium creates p-type extrinsic material portions in a semiconductor wafer. The ion beam is generally scanned across the surface of the semiconductor wafer to implant the ions from the source material, and the scanning is typically performed by a scanning component.
In a single wafer ion implantation system with scanned beam, uniformity correction is typically achieved by varying the scan speed. This requires a high bandwidth scanner. In magnetically-scanned systems, this requirement can be difficult to meet due to eddy-current losses, among other factors. In both magnetic and electrostatic systems, the beam neutralization in the scanner region can change markedly as the scan field passes through zero. This beam neutralization change can cause the beam size to change and the beam current to change. These changes are called the zero field effects (ZFE). The ZFE are typically small and not much of a problem in medium-current and high energy systems because the beam is typically at fairly high energies through the scanner. In magnetically-scanned high current beamlines, the ZFE can be dramatic with the beam current changing drastically and shrinking in size by a comparable amount. Consequently, this puts a heavy demand on the dynamic range of the scanner and requires sophisticated correction algorithms. There is therefore a need for a simple way to avoid the downsides of ZFE while taking advantage of the simplicity of bipolar scanning.